In a disk drive, while the disk drive is operating, the read/write head is positioned over the disk file. During operation, the magnetic-transducer's smooth slider air-bearing surface does not come into contact with the disk's surface. However, when the disk drive is turned off, the magnetic-transducer's air-bearing surface is parked on the start/stop zone of the disk where data is not kept. The start/stop zone is an annular area of the disk which is toward the inner diameter of the disk. The transducer's air-bearing surface comes into direct contact with the start/stop zone. To avoid stiction of the magnetic-transducer's smooth slider air-bearing surface when the parked read/write head is activated for operation, the start/stop zone as well as the entire surface of the disk is textured.
Commonly, disk texturing is provided in the following manner. The aluminum-alloy disk substrate of a magnetic-recording disk is coated with an electroless-deposited nickel-phosphorus alloy, which is nonmagnetic. The surface of the electroless-deposited-nickel-phosphorus-alloy-coated aluminum-alloy disk is lapped and polished prior to the subsequent plating or sputter-deposition of the magnetic layer. After polishing, the nickel-phosphorus-alloy-coated aluminum-alloy disk is textured by very light abrasion to provide a circumferential scratch pattern by pressing the disk against a rotating surface containing fine particles of alumina (corundum) (Al.sub.2 O.sub.3) or of silicon carbide (SiC).
The process for obtaining this circumferential scratch pattern provides two distinct functions. First, the circumferential texturing grooves assist in alignment of the crystallites of the subsequently sputter-deposited chromium and cobalt-alloy thin-film layers with grain-boundary matching between these layers and the texture grooves. This phenomenon leads to an in-plane circumferential versus radial anisotropy, improving the read-signal parametrics of anisotropic cobalt-alloy films.
The second function of the circumferential scratch pattern is to provide adequate texturing in the start/stop zone. As noted above, in disk drives, the magnetic-transducer's smooth slider air-bearing surface comes into contact with the disk surface when the drive is turned off. Such texturing helps to avoid stiction of the head to the disk.
The head's slider material is usually a composite of aluminum oxide (Al.sub.2 O.sub.3) and titanium carbide (TiC) and the load force on this slider against the disk can range from 5 to 12 grams. Typically, the textured surface is coated with outer layers consisting of a 100 nm layer of chromium (Cr), a 60 nm layer of magnetic material, a 20-30 nm layer of carbon (C), and a 2-3 nm layer of lubricant. Because these outer layers are very thin and provide very little protection against wear when the head comes into contact with the disk surface when the drive is turned off, the disk start/stop surface can become smoother after a few thousand contact start/stop cycles. Therefore, even though texturing had been initially provided, the start/stop zone may in fact become worn out. Then, when the drive is turned off and the two smooth surfaces come into contact, the friction at the head/disk interface will increase. This frictional force can reach a level where the transducer becomes stuck to the disk, causing the disk drive to fail due to the motor not having enough power to free the surfaces or to the motor starting force causing permanent damage to both surfaces.
Should deeper texturing grooves be used to provide a higher surface roughness which will assist in reducing friction at the head/disk interface, an increase of the flying height of the transducer in the data zone would result. The peak-to-valley height of exaggerated texturing grooves would become higher than the desired flying height of the transducer. Such a configuration would provide a serious limiting factor, in that drive designers seek configurations allowing the transducer to fly closer to the disk, therefore providing an increase in storage density.